This invention relates to a process for preparing a chromium-containing catalyst for the polymerization of olefins, comprising applying to an inert inorganic support a chromium complex of one or more organometallic compounds of a metal of group II or III of the periodic table in which hydrocarbyl groups having 1-20 carbon atoms are bonded to this metal.
The invention relates also to the polymerization with such a catalyst of an .alpha.-olefin having 2-8 carbon atoms, in particular ethylene, and optionally including up to 15 mole % of one or more other .alpha.-olefins having 2-15 carbon atoms.
Such processes are known from U.S. Pat. No. 4,146,695, and are described in the co-pending Application Ser. No. 320,563 filed Nov. 12, 1981.
Additionally, from U.S. Pat. No. 3,951,933 and from the Russion Pat. Nos. 269,151 and 433,172 it is known to add nickel oxide to chromium-oxide-containing catalysts, either to prevent the formation of unsaturation in the polymers or copolymers obtained or to obtain polymers of lower density by dimerization of the monomer.
Polymerizations of olefins, and in particular ethylene, according to known processes, can be carried out as a `solution process`, a `suspension process` or a `gas-phase process`, to yield polymers of relatively high density. The polymers obtained with known chromium-containing catalysts have generally been found to exhibit a relatively wide molecular weight distribution. However, for certain applications it is desirable to obtain polymers having high density, but having the narrowest possible molecular weight distribution. This is notably the case for applications such as injection molding of polyethylene.